To control a bank of elevators, a group control apparatus is typically used to efficiently run these elevators. In some elevator systems, a plurality of cars serve in a single shaft. Different from an elevator system where only a single car serves in each shaft, such an elevator system requires its group control apparatus to not only raise the transportation efficiency but also avoid collision between them. An example of such a prior art group control apparatus is an operation control apparatus employed in a multi-car elevator system as described in Japanese Patent No. 3029168. This operation control apparatus always checks the current position of the front car and the stoppable position of the rear car and, if the stoppable position of the rear car enters a zone of a certain length assumed behind the front car, this apparatus controls to stop the rear car. Although it is therefore possible to avoid collision between the cars, the rear car must be stopped to prevent collision. In addition, since this operation control apparatus assumes application to a circulation-type elevator system including an up-only shaft and a down-only shaft, it is not possible to lift up and down each car independently, making it difficult to raise the transportation efficiency as an elevator system.
In the case of an elevator group control apparatus disclosed in Japanese Patent Laid-Open No. 2001-335244, if a new destination floor is entered, the elevator group control apparatus computes the expected positional transition of a car at a desired time taken until the desired car reaches the destination floor inputted and those of the other cars in the same shaft and predicts whether the car would collide with another car before it reaches the destination floor. Based on the result of such predictions, the elevator group control apparatus determines which car is to be assigned to the new destination floor call. However, since this assignment is determined based on predictions subject to calculation errors, etc., there remains a possibility that the car assigned to the new destination floor call may collide with another car. Therefore, to avoid collision between cars, emergency stop is required. This makes it difficult to improve the operation efficiency.
The present invention solves the above-described conventional problems with an elevator system having two cars capable of going up and down independently in each shaft. Control according to the present invention can reliably avoid collision between cars serving in the same shaft while efficiently operating the same bank of plural elevators.